﻿Yol. 64.] LAUKENTIAN SYSTEM IN EASTEEN CANADA. 131 



granite-magma from below, and these foci indicate the axis of 

 greatest upward movement and that along which the granite-magma 

 has been supplied most rapidly.. 



These centres are not, however, in all cases areas of more rapid 

 uplift ; but, on the contrary, the gneissic foliation in some cases dips 

 inward in all directions towards the centre, thus marking them as 

 places where the uprise of the magma was impeded, being there 

 slower than in the adjacent portions of the district — that is to say, 

 places where the overlying strata have sagged down into the granite- 

 magma. 



If this district presents the basement of a foriner mountain-range 

 now planed down, the direction of this mountain-range was about 

 N. 30° E., or in a general way parallel to the course of the valley 

 of the St. Lawrence. 



The movements in the granite to which reference has been made 

 did not take place solely while the rock was in the form of an 

 uncrystallized or glassy magma. They continued as the rock cooled 

 and while it was filled with abundant products of crystallization, 

 the movement being brought to a close only by the complete 

 solidification of the rock. Evidence of protoclastie structure can 

 therefore be seen throughout all the areas coloured as granite 

 or granite-gneiss in the map, except in the case of a few small 

 bodies of granite apparently of more recent age. This protoclastie 

 structure is marked by the presence of more or less lenticular, 

 broken fragments of large individuals of the felspar, in a fluidally- 

 arranged mosaic of smaller allotriomorphic felspar-grains with 

 quartz-strings and a few biotite-flakes. This fluidal arrangement, 

 which constitutes the foliation of these rocks, is seen in every 

 stage of development, there being an imperceptible gradation from 

 the perfectly-massive forms occasionally seen, through the more or 

 less gneissic varieties, to thinly-foliated gneisses. It is impossible to 

 separate the several varieties. They constitute progressive develop- 

 ments of one and the same structure, and are different phases of 

 one and the same rock-mass. 



The granite-gneiss is undoubtedly of igneous origin, is very 

 uniform iu its mineralogical composition, and differs distinctly from 

 the sedimentary gneisses or paragneisses of the area. It is medium 

 to rather fine in grain, and composed almost .entirely of quartz and 

 felspar, the latter preponderating. Some biotite is present, but in 

 very subordinate amount. The rock in the southern bathyliths 

 occasionally contains a little hornblende. While the felspar is 

 always reddish in colour, a large proportion of it is really an acid 

 oligoclase. The rock ■ would ordinarily be classed as an albite- 

 granite or granite-gneiss, and, although the lime-soda felspar 

 preponderates, should be so classed, since it resembles a granite in 

 every respect. 



Two analyses of typical specimens of this granite are tabulated 

 on the following page : — 



